/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.jn.langx.escape;


import com.jn.langx.annotation.Nullable;
import com.jn.langx.util.Preconditions;

import java.util.Map;

/**
 * A {@link UnicodeEscaper} that uses an array to quickly look up replacement characters for a given
 * code point. An additional safe range is provided that determines whether code points without
 * specific replacements are to be considered safe and left unescaped or should be escaped in a
 * general way.
 * <p>
 * <p>A good example of usage of this class is for HTML escaping where the replacement array
 * contains information about the named HTML entities such as {@code &amp;} and {@code &quot;} while
 * {@link #escapeUnsafe} is overridden to handle general escaping of the form {@code &#NNNNN;}.
 * <p>
 * <p>The size of the data structure used by {@link ArrayBasedUnicodeEscaper} is proportional to the
 * highest valued code point that requires escaping. For example a replacement map containing the
 * single character '{@code \}{@code u1000}' will require approximately 16K of memory. If you need
 * to create multiple escaper instances that have the same character replacement mapping consider
 * using {@link ArrayBasedEscaperMap}.
 */
public abstract class ArrayBasedUnicodeEscaper extends UnicodeEscaper {
    /**
     * The replacement array (see ArrayBasedEscaperMap).
     */

    private final char[][] replacements;
    /**
     * The number of elements in the replacement array.
     */
    private final int replacementsLength;
    /**
     * The first code point in the safe range.
     */
    private final int safeMin;
    /**
     * The last code point in the safe range.
     */
    private final int safeMax;

    /**
     * Cropped values used in the fast path range checks.
     */
    private final char safeMinChar;
    private final char safeMaxChar;

    /**
     * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement map and specified
     * safe range. If {@code safeMax < safeMin} then no code points are considered safe.
     * <p>
     * <p>If a code point has no mapped replacement then it is checked against the safe range. If it
     * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed.
     *
     * @param replacementMap    a map of characters to their escaped representations
     * @param safeMin           the lowest character value in the safe range
     * @param safeMax           the highest character value in the safe range
     * @param unsafeReplacement the default replacement for unsafe characters or null if no default
     *                          replacement is required
     */
    protected ArrayBasedUnicodeEscaper(
            Map<Character, String> replacementMap,
            int safeMin,
            int safeMax,
            @Nullable
                    String unsafeReplacement) {
        this(ArrayBasedEscaperMap.create(replacementMap), safeMin, safeMax, unsafeReplacement);
    }

    /**
     * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement map and specified
     * safe range. If {@code safeMax < safeMin} then no code points are considered safe. This
     * initializer is useful when explicit instances of ArrayBasedEscaperMap are used to allow the
     * sharing of large replacement mappings.
     * <p>
     * <p>If a code point has no mapped replacement then it is checked against the safe range. If it
     * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed.
     *
     * @param escaperMap        the map of replacements
     * @param safeMin           the lowest character value in the safe range
     * @param safeMax           the highest character value in the safe range
     * @param unsafeReplacement the default replacement for unsafe characters or null if no default
     *                          replacement is required
     */
    protected ArrayBasedUnicodeEscaper(
            ArrayBasedEscaperMap escaperMap,
            int safeMin,
            int safeMax,
            @Nullable String unsafeReplacement) {
        // GWT specific check (do not optimize)
        Preconditions.checkNotNull(escaperMap);
        this.replacements = escaperMap.getReplacementArray();
        this.replacementsLength = replacements.length;
        if (safeMax < safeMin) {
            // If the safe range is empty, set the range limits to opposite extremes
            // to ensure the first test of either value will fail.
            safeMax = -1;
            safeMin = Integer.MAX_VALUE;
        }
        this.safeMin = safeMin;
        this.safeMax = safeMax;

        // This is a bit of a hack but lets us do quicker per-character checks in
        // the fast path code. The safe min/max values are very unlikely to extend
        // into the range of surrogate characters, but if they do we must not test
        // any values in that range. To see why, consider the case where:
        // safeMin <= {hi,lo} <= safeMax
        // where {hi,lo} are characters forming a surrogate pair such that:
        // codePointOf(hi, lo) > safeMax
        // which would result in the surrogate pair being (wrongly) considered safe.
        // If we clip the safe range used during the per-character tests so it is
        // below the values of characters in surrogate pairs, this cannot occur.
        // This approach does mean that we break out of the fast path code in cases
        // where we don't strictly need to, but this situation will almost never
        // occur in practice.
        if (safeMin >= Character.MIN_HIGH_SURROGATE) {
            // The safe range is empty or the all safe code points lie in or above the
            // surrogate range. Either way the character range is empty.
            this.safeMinChar = Character.MAX_VALUE;
            this.safeMaxChar = 0;
        } else {
            // The safe range is non empty and contains values below the surrogate
            // range but may extend above it. We may need to clip the maximum value.
            this.safeMinChar = (char) safeMin;
            this.safeMaxChar = (char) Math.min(safeMax, Character.MIN_HIGH_SURROGATE - 1);
        }
    }

    /**
     * This is overridden to improve performance. Rough benchmarking shows that this almost doubles
     * the speed when processing strings that do not require any escaping.
     */
    @Override
    public final String escape(String s) {
        // GWT specific check (do not optimize)
        Preconditions.checkNotNull(s);
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if ((c < replacementsLength && replacements[c] != null) || c > safeMaxChar || c < safeMinChar) {
                return escapeSlow(s, i);
            }
        }
        return s;
    }

    /**
     * Escapes a single Unicode code point using the replacement array and safe range values. If the
     * given character does not have an explicit replacement and lies outside the safe range then
     * {@link #escapeUnsafe} is called.
     */
    @Override
    protected final char[] escape(int cp) {
        if (cp < replacementsLength) {
            char[] chars = replacements[cp];
            if (chars != null) {
                return chars;
            }
        }
        if (cp >= safeMin && cp <= safeMax) {
            return null;
        }
        return escapeUnsafe(cp);
    }

    /**
     * Overridden for performance.
     */
    @Override
    protected final int nextEscapeIndex(CharSequence csq, int index, int end) {
        while (index < end) {
            char c = csq.charAt(index);
            if ((c < replacementsLength && replacements[c] != null) || c > safeMaxChar || c < safeMinChar) {
                break;
            }
            index++;
        }
        return index;
    }

    /**
     * Escapes a code point that has no direct explicit value in the replacement array and lies
     * outside the stated safe range. Subclasses should override this method to provide generalized
     * escaping for code points if required.
     * <p>
     * <p>Note that arrays returned by this method must not be modified once they have been returned.
     * However it is acceptable to return the same array multiple times (even for different input
     * characters).
     *
     * @param cp the Unicode code point to escape
     * @return the replacement characters, or {@code null} if no escaping was required
     */
    protected abstract char[] escapeUnsafe(int cp);
}
